Process for the continuous deposition of a protective layer on forged,rolled or foundry products

ABSTRACT

METALLIC FORGED, ROLLED OR FOUNDRY PRODUCTS ARE DEOXIDIZED OR DESCALED BY APPLYING TO SUCH PRODUCTS, WHILE THEY ARE HOT, A SUITABLE REDUCING AGENT AND, WHILE THE PRODUCTS ARE MAINTAINED IN A HEATED STATE, APPLYING A PROTECTIVE AGENT, CAPABLE OF EXISTING IN DIFFERENT PHYSICAL, CHEMICAL OR ELECTRICAL STATES. THE REDUCING AGENT MAY BE A BORON, PHOSPHORUS, SILICON OR ALUMINUM DERIVATIVE. THE PROTECTIVE AGENT MAY BE A METAL SUCH AS A FERRO METAL SUCH AS FERRO-MANGANESE, FERRO-SILICON, AN OXIDE OR A MINERAL OR CHEMICAL PRODUCT AND MAY BE PROJECTED ONTO THE PRODUCT IN POWDER FORM. IT MAY FORM A CHEMICAL OR ALLOY BOND WITH THE BASE METAL OF THE PRODUCT TO FORM AN OXIDATION- OR CORROSION-RESISTANT COATING.

United States Patent Office 3,690,913 Patented Sept. 12, 1972 PROCESS FOR THE CONTINUOUS DEPOSITION OF A PROTECTIVE LAYER ON FORGED, ROLLED OR FOUNDRY PRODUCTS Georges Schaumburg, l-bis, Rue de Londres, Montignyles-Metz, Moselle, France No Drawing. Continuation-impart of application Ser. No. 714,419, Mar. 20, 1968. This application Nov. 9, 1970, Ser. No. 88,211 Claims priority, applicz itgio il8 France, Mar. 31, 1967,

Int. (:1. (323a 3/00 US. Cl. 117-43 9 Claims ABSTRACT OF THE DISCLOSURE Metallic forged, rolled or foundry products are deoxidized or descaled by applying to such products, while they are hot, a suitable reducing agent and, while the products are maintained in a heated state, applying a protective agent, capable of existing in different physical, chemical or electrical states. The reducing agent may be a boron, phosphorus, silicon or aluminum derivative. The protective agent may be a metal such as a term metal such as ferro-manganese, ferro-silicon, an oxide or a mineral or chemical product and may be projected onto the product in powder form. It may form a chemical or alloy bond with the base metal of the product to form an oxidation or corrosion-resistant coating.

CROSS-REFERENCE TO OTHER APPLICATIONS This application is a continuation-in-part of US. application Ser. No. 714,419, filed Mar. 20, 1968 now abandoned.

BACKGROUND OF THE INVENTION (1) Field of the invention The present invention relates to a novel process for the continuous application in the heated state of a protective layer on forged, rolled or foundry products.

(2) Description of the prior art It is known that the effects of atmospheric oxidation or corrosive action on metallic surfaces may be reduced by the application of a coating to the surface, the purpose of which is to isolate the surface from contact with any atmosphere capable of contaminating or attacking it. It is further known that application of such protective coatings, regardless of whether the metal is cold or in a heated state, must be preceded by a deoxidation treatment in order to ensure sufficient anchorage of the coating. The necessity for carrying out such a separate deoxidation treatment results in a relatively costly operation.

Accordingly, the present invention has for its principal object avoiding this disadvantage by depositing on the metallic surface of the product, while hot, in the course of processing and without the necessity of providing special billet-handling means, a protective layer of suitable quality and of assuring good anchorage of this protective layer to the base surface. The products treated by the present invention are preferably ferrous metals, such SUMMARY OF THE INVENTION According to the process of the present invent-ion, a two-step process is employed wherein, in the first step, the product, While in the heated state, is subjected to a descaling operation by contact with a reducing agent. In the second step of the present process, there is applied, while the product is maintained in the same heated state,

a protective agent capable of existing in different physical, chemical or electrical states. The protective layer is thus deposited continuously during the production process without necessitating special billet-handling means. By the present process, good anchorage of the protective coating to the metallic surface is assured and, in certain cases, diffusion of the protective coating into the metallic surface is obtained.

DETAILED DESCRIPTION OF THE INVENTION The process of the present invention has particular applicability to the cleaning and protecting of steel, which is ordinarily subjected to temperatures between 900 and 1200 C. during the usual hot rolling operation.

Contrary to prior art processes, the present invention may be practiced employing existing rolling mill equipment and without extensive modification thereof. For example, all that is necessary to practice the present invention employing conventional equipment is the addition of a transverse tube provided with spray nozzles and connected to sources of reducing agent and coating material. No other preferential circuit (special billet-handling means) is required.

In one specific embodiment of apparatus by which the process of the present invention may be practiced, there is provided, after the last cage of the rolling mill, a transverse spray tube. This spray tube is provided with multiple spray nozzles (either 4 or 8). The diameter of each nozzle is millimeters and the diameter of the tube is to millimeters. In this embodiment the coating material (powder) is emulsified with a reducing gas, e.g., hydrogen or nitrogen, and the mixture projected through the nozzle. In an alternate and preferred embodiment, a tube may be provided which possesses eight spray nozzles connected to a coating material (powder) source and four nozzles connected to a reducing gas source.

The length of the spray tube employed should be such as to permit a billet processing time, i.e., the period of time during which the product contacts the chemical environment of the coating material and the reducing gas, of about 0.1 to 0.2 second. In general, the minimum tube length would be about 1.50 m. for a slower moving billet and longer for a faster moving product such as a wire.

The number of spray nozzles which may be employed is that quantity which is sufficient to produce a powder flow of at least about 30 g./m. on the billet. Each spray nozzle is Venturi-shaped. The nozzle axis of each nozzle is inclined 15 from the longitudinal axis and 30 from the vertical plane in order to produce a turbulent condition. The Venturi elfect obtained by the use of such nozzles permits the obtaining of an impact speed of the powder on the billet of 10 m./sec., employing a gaseous pressure of 4 bars. A suitable feed rate of, for example, a mixture of coating powder and gas to the nozzles is about 6 m./sec.

When employing a spray tube provided with nozzles for both the coating material and a reducing gas, the minimal length of the tube should be about 3.0 m.

The temperatures of the process generally range from 700 C. to 1100 C. with the process being operated at pressures of 1.5 kg./cm. to 5 kg./cm. depending upon the processing speed and temperature. For example, a product heated to a temperature of 100 C. and being rolled at a speed of 400 m./sec. employs a pressure of 5 kg./cm. whereas with a product at a temperature of 800 C. and a rolling speed of 2 m./ sec. a pressure of 2.5 kg./cm. can be satisfactorily used.

The process is conducted in the absence of water and moisture since the powders used hydrolyze easily and are somewhat hygroscopic. The billets subjected to the process have been previously treated to a descaling step either using mechanical descaling, for example, resulting from the last rolling pass, or using water under pressure. For example, as indicated above, after the last rolling pass, giving rise to, in addition, a mechanical descaling effect, the tubes are installed whereby the process of this invention is accomplished on a surface with a minimum amount of scale. The scale remaining is first reduced and on this surface the mineral compositions described hereinafter are projected onto the surface. Sufiicient kinetic force is generated to project the particles onto the surface with the necessary speed to overcome any air resistance due to the movement of the product. The particles reaching the surface subsequently melt providing a coating which prevents contact with oxygen.

As coating compositions of the present invention, there may be mentioned a wide variety of materials which possess the necessary chemical and physical properties required to insure the desired protective and reducing rolls. That is, the materials to be employed in the process of the present invention are those which form a pellicle when heated, suppress oxide formation on the surface of the metal to be protected and which form a film through which the surface of the metal can be observed. Such materials can comprise either mineral or organic components.

As mineral compositions which have been found to be suitable for use in the process of the present invention, there may be mentioned:

(a) Si A1 0 CaO, MgO, Na, K, and B 0 S102, KBOg, NH2CO3, and B203;

(0) S102, KBO2, Na CO NaNH and H3P04; (d) SiO A1 0 C210, and MgO;

(e) Na2B407, S102, and Gao- The above mixtures, as well as those of the following examples, have been found to be absolutely non-toxic and very eflicient in the protection of steel at forging temperatures of between 900 and 1200 C.

As indicated above, the billet is preferably subjected to a descaling step, however, these compositions can be used, if desired, on surfaces possessing scale.

As organic compositions which have been found to be suitable for use in the process of the present invention, there may be mentioned mixtures of cellulose, a vegetable oil, such as palm nut oil, arachis oil, sunflower oil or the like, together with at least one material selected from among bentonite clay, chalk or carbon black.

In addition to the SiO A1 0 or H PO also useful in the obtaining of a surface enamel in accordance with the present invention is zinc borate. The use of zinc borate may also result in the presence of an underlayer produced from the diffusion of the zinc into the basic metal.

The reducing gas which may be employed in the process of the present invention may be, for example, boron methyl admixed with vapors of zinc, chromium, nickel, manganese and the like, or with nitrogen or hydrogen. B 0 or Na B O can be used Where desired.

The protective coating produced by application of the above materials dissolves the residual oxide on the metal surface within an unorganized crystallographic system, thus avoiding the destruction of the protective layer by means of the mechanical action of the rollers. The principle of this operation is similar for other powders forming products possessing a space lattice, that is, products possessing an ionic potential of about 7 or higher, such as silicon, phosphorus, arsenic, boron and beryllium.

The use of the term electrical states hereinbefore in the specification relates to the anodizing of metallic surfaces in order to provide a temporary immunity against oxidation.

The following illustrative examples will more clearly indicate the nature and operation of the process of the present invention.

EXAMPLES 1 to 3 Example C SlOz A F910 MgO B K Na The sectional steel bar thus obtained possessed a protective coating resulting from the chemical combination of each of the above compositions with the base metal.

EXAMPLE 4 The procedure of Examples 1 to 3 was followed except that the following organic composition was sprayed onto the sectional bar in a form of a sprayable paste prepared by mixing the following composition with alcohol.

Proportion Ingredient: (weight percent) Cellulose 30 Palm nut oil 24 Bentonite clay 21 Carbon black 25 An excellent protective coating was produced which was easily removed after the metal had cooled.

As can be seen from the above examples, the coating compositions of the present invention are generally solid and may be employed in the form of a cloud of a very fine powder, the particles of which melt upon contact with the hot part of the liquid metal. The reducing agents can be directly gasified so as to constitute an atmosphere which possesses the property of reducing oxides.

It will be understood that the process which has been described can be used in all industries utilizing oxidizable metals. It is especially suitable for use in the iron and steel industry, in forges or in foundries.

What is claimed is:

1. A process for continuously coating a protective layer on a forged, rolled or foundry product consisting essentially of iron or steel to inhibit oxidation thereof comprising:

(a) subjecting said product, in the absence of water,

to a gaseous reducing atmosphere to descale the surface thereof by reducing the same; and

(b) applying, in the absence of water, to the resulting surface-reduced product a mineral or organic compound coating composition which forms pellicles when heated, suppresses oxide formation on the surface-reduced product and forms a film through which the surface of the product can be observed; wherein each of steps (a) and (b) is performed at a temperature of from 700 to 1100 C. and at a pressure of from 1.5 to 5 kilograms per square centimeter; said gaseous reducing atmosphere comprising a mixture of boron methyl with nitrogen, hydrogen or vapors of zinc, chromium, nickel or manganese.

2. The process of claim 1 wherein the mineral or organic compound coating composition is applied to the surface-reduced product in powder form.

3. The process of claim 1 wherein said mineral composition is selected from the group consisting of compositions having the following ingredients:

(a) SiO A1 0 CaO, MgO, Na, K and B 0 (b) Si0 ,KBO Na CO and B 0 (C) S102, KBOZ, Na CO NHNH4, and H3PO4; (d) SiO A1 0 CaO, and MgO;

(e) Na B.,O SiO and CaO.

4. The process of claim 1 wherein said organic composition comprises a mixture of cellulose, a vegetable oil and at least one material selected from the group consisting of bentonite clay, chalk and carbon black.

5. The process of claim 3, wherein said mineral composition further comprises zinc borate.

6. The process of claim 1 wherein said mineral composition comprises the following approximate composition: 17.5 parts by weight CaO, 5.5 parts by weight SiO 1.4 parts by weight A1 0 0.5 part by Weight Fe 0 1.6 parts by Weight MgO, 14 parts by weight B, 0.5 part by weight K and 0.3 part by weight Na.

7. The process of claim 1 wherein said mineral composition comprises the following approximate composition: 16.0 parts by weight CaO, 4.5 parts by weight SiO 3,6 parts by weight A1 0 0.8 part by weight Fe o 2.4 parts by weight MgO and 17 parts by weight B.

8. The process of claim 1 wherein said mineral composition comprises the following approximate composition: 25.0 parts by weight CaO, 7.0 parts by weight SiO 4.2 parts by weight A1 0 1.2 parts by weight Fe O 3.2 parts by weight MgO and 17 parts by weight Na.

9. The process of claim 1 wherein said organic com- References Cited UNITED STATES PATENTS 2,442,485 6/ 1948 Cook 117-50 3,040,103 6/1962 Joly et a1. 260-6065 B 1,996,840 4/1935 Staley 1l723 FOREIGN PATENTS 2,011,652 3/1970 France.

1,527,030 4/1968 France.

RALPH S. KENDALL, Primary Examiner US. Cl. X.R. 

